1. Field of the Invention
The present invention relates to a mechanism for holding the hub of a removable disk cartridge to the spindle motor of a disk drive.
2. Description of the Prior Art
Removable disk cartridges for storing digital electronic information typically comprise an outer casing or shell that house one or more rotatable storage media, or disks, upon which electronic information can be stored. The cartridge shell often comprises upper and lower halves that are joined together to house the disk(s). The disk(s) is mounted on a hub assembly that rotates freely within the cartridge. The outer shell of the cartridge typically has some form of opening near its forward edge to provide the recording heads of the drive with access to the recording surfaces of the disk. A shutter or door mechanism is provided to cover the opening when the cartridge is not in use to prevent dust or other contaminants from entering the cartridge and settling on the recording surface of the disk.
When the cartridge is inserted into a data storage device, i.e., disk drive, a spindle motor in the drive engages the hub assembly through an opening in the bottom shell of the disk cartridge in order to rotate the disk within the cartridge. In many prior art removable cartridge disk drive systems, a center spindle on the motor engages a hub assembly. A chucking magnet in the spindle and/or hub assembly provides sufficient force to keep the hub assembly engaged on the spindle motor during rotation. Magnetic chucking provides sufficient engagement in most disk drives that operate at lower rotations speeds, as well as in most disk drive units that are internally mounted in a computer casing.
A locking mechanism such as that described in U.S. Pat. No. 5,757,584, Schick, is sometimes provided to lock the disk cartridge hub to the spindle motor. However, the magnetic chucking assembly may be useful to hold the cartridge to the spindle motor until the locking mechanism is engaged. (This patent shows a drive of the type commonly referred to as JAZ).
U.S. Pat. Nos. 5,617,397 and 5,805,555, Jones et al. show a cartridge of the type commonly referred to as the ZIP cartridge and a drive for use with that cartridge. The ZIP drives such as that disclosed in the aforementioned patents have a four pole magnet made from a high energy. NdFeB material with a solid stainless steel hub. The tangential holding force is adequate, but it is desirable to increase the tangential holding force without increasing the vertical holding force. An increase in vertical holding force would cause dehubbing problems that might possibly occur with a larger vertical force. This invention solves the problem.
U.S. Pat. No. 6,043,945 Muse, et al shows a cartridge and drive of the type commonly referred to as Clik! This patent is incorporated by reference herein.
An object of the present invention is to increase the tangential holding force between the magnet and the hub, without increasing the vertical holding force. A further object of the present invention is to provide a more durable magnet material than the bare sintered magnet which may abrade in use. Another objective of the invention is to reduce the expense of the hold down magnet.
In accordance with the present invention a larger tangential holding force is obtained in a hubbing mechanism by using a magnet with multiple poles and a hub which is segmented to match the number of poles in the magnet. More specifically, the hub is cut in the form of a xe2x80x9cradial combxe2x80x9d which has strips or segments cut out of it. The tangential force between the metal comb and the magnet has a pronounced ratchet effect when the comb is moved over the magnet. The tangential force is much larger when the metal strips lie over a magnetized region in the magnet. The magnetic force is smaller when the strips are over a transition in the pattern recorded in the magnet. It has been found that a segmented hub in accordance with the present invention provides significantly greater tangential force per unit area than a solid hub.
In accordance with the present invention a larger tangential force is obtained by using a magnet with multiple poles, and segmenting the hub to match the number of poles in the magnet. The vertical force holding force is not increased.
The foregoing and other objects, features and advantages of the invention will be better understood from the following more detailed description and appended claims.